The invention relates to an annular casing with a wear-resistant surface for a press roller for subjecting particulate material to pressure, in particular for roller presses for material-bed comminution. The invention also relates to a method for the production of such a press roller annular casing.
In the case of roller mills, particulate, brittle material to be ground is drawn into the roller nip, by which the two rotatably mounted, counter-rotatable rollers are separated from each other, and is subjected there to pressure comminution. Also known is so-called material-bed comminution in the roller nip of a high-pressure rolling mill, also known as a rolling press, in which the individual particles of the material to be ground that is drawn into the roller nip by friction are squeezed against one another in a bed of material, i.e. in a charge of material compressed between the two roller surfaces, when a high pressure is applied. The surfaces of the rollers thereby undergo a high level of wearing stress. Therefore, such roller surfaces have to meet at least the following requirements:
They should have high wear resistance, be able to be produced at low cost, be able to be repaired by the operator of the rolling press and also have good drawing-in characteristics for the material to be comminuted.
The article in the technical journal “ZKG International, No. 7/1997, pages 384 to 392 discloses on page 384, paragraph 1, with respect to wear protection in the case of high-pressure roller presses that roller casings of chilled cast iron may be advantageous because of their high compressive strength and that long service lives of the roller press can be achieved with casings of alloyed nodular cast iron, the term nodular cast iron being understood in material science as meaning cast iron with nodular graphite. Furthermore, it is known from the reprint from the technical journal “konstruieren+giessen” 1988, No. 1, from the Zentrale für Guβverwendung, Dusseldorf, with the article “Gusseisen mit Kugelgraphit” [cast iron with nodular graphite] (ductile cast iron), pages 13-16, to impart high ductility and compressive strength to the nodular cast iron by a special heat treatment, known as bainitic hardening.
It is known from EP-A 0 563 564 and EP-A 0 916 407 to produce the chilled cast-iron roller shell of a grinding roller from a bainitic cast iron alloy and, in order to increase the wear resistance and the ability to draw in material to be ground, to apply a surface profiling of hard surfacing materials on the outer circumferential surface of the roller shell. Although surfacing beads are capable of helping to improve the characteristics for drawing in feedstock, they are not capable of autogenous wear protection, because surfacing beads with their typical rounded profile cannot detain for any length of time the material that gets into the interstices between the beads.
Finally, it is known from EP-B 0 516 952, FIG. 2, to make the roller surface of roller presses more resistant to wear by arranging on the roller surface a multiplicity of prefabricated hard metal bodies, such as stud bolts for example, which can be incorporated in corresponding blind-hole bores of the roller shell. In the case of this so-called grid armouring, stud bolts protrude outward from the roller surface to such a great height and are arranged at such a distance from one another that, when the roller press is in operation, on the roller surface the interstices between the stud bolts remain filled with the pressed-together fine-grained material, which forms autogenous wear protection for the roller surfaces and, on account of its roughness, also has good drawing-in characteristics. This known roller surface reinforcement with alternating zones of highly wear-resistant material and intermediate spatial zones of other wear resistance has proven to be successful in practice in the material-bed comminution of ore material in particular.